Oil Separators

ABSTRACT

An oil separator for trapping oil mist contained in blow-by gas includes a separation plate, an upstream oil-mist trapping chamber, and a downstream oil-mist trapping chamber. The upstream and downstream oil-mist trapping chambers are divided by the separation plate. The upstream oil-mist trapping chamber communicates with a flow inlet for blow-by gas. The downstream oil-mist trapping chamber communicates with the upstream oil-mist trapping chamber and communicates with a flow outlet for blow-by gas. A return port formed through the separation plate returns oil mist trapped in the downstream oil-mist trapping chamber into the upstream oil-mist trapping chamber. The return port is positioned vertically above the bottom surface of the upstream oil-mist trapping chamber and is positioned at substantially the same vertical level as the lowermost portion of the bottom surface of the downstream oil-mist trapping chamber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese patent application serialnumber 2017-236918 filed Dec. 11, 2017, which is hereby incorporatedherein by reference in its entirety for all purposes.

BACKGROUND

The present disclosure relates to an oil separator, and morespecifically, it relates to an oil separator to trap oil mist containedin blow-by gas.

A conventional positive crankcase ventilation (PCV) system, which isemployed in an internal combustion engine like an automobile engine, isknown in the art. Air pollution may result when blow-by gas(un-combusted gas) leaks and/or is discharged from a gap between apiston ring and a cylinder wall of the engine to the exterior atmosphereduring operation of the engine. To prevent such leakage of the blow-bygas, the PCV system collects the blow-by gas and then returns thecollected blow-by gas to an air intake system. The returned blow-by gasthen undergoes re-combustion within the engine. The blow-by gas containsoil mist, which is lubricant oil such as engine oil dispersed as microparticles. The PCV system includes an oil separator designed to trap theoil mist contained in the blow-by gas and prevent the oil mist fromflowing into the air intake system. The oil separator is provided in themiddle of a flow passage that connects a crankcase and an air-intakeduct.

A conventional labyrinth-type oil separator 101, as illustrated in FIG.6, is disclosed, for example, in Japanese Laid-Open Patent PublicationNo. 2009-68471. As illustrated in FIG. 7, the oil separator 101 includesa lower base 110, a middle base 130, and an upper base 140, where thesebases 110, 130, 140 are attached to each other by vibration welding. Theoil separator 101 includes a liquid oil trapping chamber 150, a primaryoil-mist trapping chamber 151, and a secondary oil-mist trapping chamber152, where each of the chambers 150, 151, 152 is defined between two ofthe bases 110, 130, 140. The liquid oil trapping chamber 150 contains acompartmented interior space therein, which is capable of trappingliquid oil with a relatively large particle size (not shown). Theprimary oil-mist trapping chamber 151 is located downstream of theliquid oil trapping chamber 150 and contains a compartmented interiorspace therein, which is capable of trapping oil mist with a relativelysmall particle size (not shown).

As illustrated in FIG. 7, the secondary oil-mist trapping chamber 152 isarranged adjacent to the primary oil-mist trapping chamber 151 via aseparation plate 131 of the middle base 130. The secondary oil-misttrapping chamber 152 is located downstream of the primary oil-misttrapping chamber 151 and contains compartmentalized interior space,which is capable of trapping oil-mist with a relatively small particlesize. The separation plate 131 has a first communication port 132, asecond communication port 133, and a return port 134. The firstcommunication port 132 allows the liquid oil trapping chamber 150 andthe primary oil-mist trapping chamber 151 to communicate with eachother. The second communication port 133 allows the primary oil-misttrapping chamber 151 and the secondary oil-mist trapping chamber 152 tocommunicate with each other. The return port 134 allows communicationbetween the primary oil-mist trapping chamber 151 and the secondaryoil-mist trapping chamber 152, so as to allow the oil mist trapped bythe secondary oil-mist trapping chamber 152 to return to the primaryoil-mist trapping chamber 151.

Containing more than one oil-mist trapping chambers (the primaryoil-mist trapping chamber 151 and the secondary oil-mist trappingchamber 152 in this example), the oil separator provides a passagehaving a long length for the blow-by gas, which has flown into the oilseparator 101. Such a configuration of the oil separator 101, with along length of passage, can enhance trapping efficiency of the oil mistwith a small diameter. The return port 134 allows the oil-mist trappedin the secondary oil-mist trapping chamber 152 to merge with the oilmist trapped in the primary oil-mist trapping chamber 151. The merged,trapped oil may be collected together with the liquid oil trapped in theliquid oil trapping chamber 150. This configuration allows the oil-misttrapped in the secondary oil-mist trapping chamber 152 to be collectedwithout a dedicated collecting passage. As a result, the size of the oilseparator 101 may be reduced while the oil separator 101 may efficientlytrap and collect the oil mist with a small particle size.

As illustrated in FIG. 8, the return port 134 is located along thebottom surface 151 a of the primary oil-mist trapping chamber 151.Additionally, the return port 134 is located along the lowermost portion152 b of the bottom surface 152 a of the secondary oil-mist trappingchamber 152. As a result, the return port 134 may facilitate return ofthe oil-mist trapped in the secondary oil-mist trapping chamber 152 tothe primary oil-mist trapping chamber 151.

The blow-by gas, however, may contain a massive amount of the liquid oilwith a large particle size. In this case, the liquid oil with a largeparticle size may flow from the liquid oil trapping passage 150 into theprimary oil-mist trapping chamber 151 through the first communicationport 132. The liquid oil with a large particle size may subsequentlyflow through the return port 134 (i.e., shortcut) from the primaryoil-mist trapping chamber 151 into the secondary oil-mist trappingchamber 152 without passing through the second communication port 133,and may finally flow out of the oil separator 101 through an outlet port113 at the lower base 110. As a result, the liquid oil with a largeparticle size may undesirably flow into an internal combustion enginelocated downstream of the oil separator 101 and may be combusted, whichmay cause a failure of the internal combustion engine.

SUMMARY

According to one aspect of the present disclosure, an oil separator fortrapping oil mist contained in blow-by gas includes a separation plate,an upstream oil-mist trapping chamber, and a downstream oil-misttrapping chamber. The upstream and downstream oil-mist trapping chambersare divided by the separation plate and are positioned adjacent to eachother. The upstream oil-mist trapping chamber communicates with a flowinlet for blow-by gas. The downstream oil-mist trapping chambercommunicates with the upstream oil-mist trapping chamber and a flowoutlet for blow-by gas. A return port is configured to return oil misttrapped in the downstream oil-mist trapping chamber back into theupstream oil-mist trapping chamber. The return port is formed throughthe separation plate. The return port is positioned above the bottomsurface of the upstream oil-mist trapping chamber and is positioned atsubstantially the same vertical level as the lowermost portion of thebottom surface of the downstream oil-mist trapping chamber.

The oil contained in blow-by gas is separated from the blow-by gas anddrops in both of the upstream and downstream oil-mist trapping chambers.The oil dropped in the downstream oil-mist trapping chamber is allowedto pass through the return port to the upstream oil-mist trappingchamber. On the other hand, the oil dropped in the upstream oil-misttrapping chamber is prevented from passing through the return port andflowing into the downstream oil-mist trapping chamber. Consequently, theliquid oil gathers in the upstream oil-mist trapping chamber and doesnot accumulate in the downstream oil-mist trapping chamber.Consequently, the liquid oil is prevented from flowing out of thedownstream oil-mist trapping chamber through the flow outlet andsubsequently being discharged to the outside. As a result, the liquidoil is prevented from flowing to a device(s) such as an internalcombustion engine positioned downstream of the oil separator and frombeing combusted in the internal combustion engine. In this way, thisconfiguration may prevent a device(s) located downstream of the oilseparator from being broken down.

According to another aspect of the present disclosure, the separationplate includes a wall surface facing opposite to the upstream oil-misttrapping chamber. The wall surface may be formed with a rib in thevicinity of the return port. The rib is configured to prevent blow-bygas from flowing into the return port through the return port.Consequently, blow-by gas is prevented from flowing from the upstreamoil-mist trapping chamber through the return port into the downstreamoil-mist trapping chamber. Thus, the blow-by gas tends not to flowthrough the return port but through a communication port thatcommunicates the upstream oil-mist trapping chamber with the downstreamoil-mist trapping chamber, from the upstream oil-mist trapping chamberto the downstream oil-mist trapping chamber.

According to another aspect of the present disclosure, the rib may havea substantially U-shaped form. For example, the rib may extend along thereturn port. Therefore, the blow-by gas may be prevented from flowingfrom the upstream oil-mist trapping chamber through the return port intothe downstream oil-mist trapping chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an oil separator according to oneexemplary embodiment.

FIG. 2 is an exploded view of the oil separator of FIG. 1.

FIG. 3 is a front view of a middle base of the oil separator of FIG. 2.

FIG. 4 is a cross-sectional view of the oil separator of FIG. 1 takenalong a line IV-IV of FIG. 3.

FIG. 5 is a schematic view of an interior of the oil separator of FIG.1.

FIG. 6 is a perspective view of a conventional oil separator.

FIG. 7 is an exploded view of the conventional oil separator of FIG. 6.

FIG. 8 is a schematic view of an interior of the conventional oilseparator of FIG. 6.

DETAILED DESCRIPTION

As previously described, in some conventional oil separators, the liquidoil with a large particle size may undesirably flow into an internalcombustion engine located downstream of the oil separator and may becombusted. Thus, there has been a need of an oil separator capable of:preventing liquid oil contained in blow-by gas from flowing into adevice located downstream of the oil separator, and thereby suppressinga failure of the device even when the blow-by gas contains a massiveamount of the liquid oil with a large particle size.

Hereinafter, an exemplary embodiment will be described with reference toFIGS. 1 to 5. As illustrated in FIGS. 1 and 2, an oil separator 1 is alabyrinth-type separator, and comprises a lower base 10, a middle base30, and an upper base 40.

As illustrated in FIG. 2, the lower base 10 is a casing member having arecess 10 a at a bottom and an opening 10 b facing the middle base 30. Afirst flow inlet 11 and a second flow inlet 12 are formed on a lowerportion of the recess 10 a to allow blow-by gas (not illustrated) toflow into the oil separator 1. A flow outlet 13 is formed on an upperportion of the lower base 10 to allow the blow-by gas to flow out of theoil separator 1. A first collision wall 14, a second collision wall 15,a third collision wall 16, a fourth collision wall 17, a fifth collisionwall 18, and a sixth collision wall 19 are formed within the recess 10a.

As illustrated in FIGS. 3 and 4, the middle base 30 is a panel membersized and shaped to cover the opening 10 b of the lower base 10. A lowerregion of the middle base 30 defines a liquid oil trapping chamber 50 incooperation with the lower base 10. The upper region of the middle base30 defines a secondary oil-mist trapping chamber 52 in cooperation withthe lower base 10. The middle base 30 defines the secondary oil-misttrapping chamber 52 and has a separation plate 31, which separates thesecondary oil-mist trapping chamber 52 from a primary oil-mist trappingchamber 51. The primary oil-mist trapping chamber 51 and the secondaryoil-mist trapping chamber 52 are arranged adjacent to each other, to theleft and right of the separation plate 31, respectively. A firstcommunication port 32, which allows the liquid oil trapping chamber 50to communicate with the primary oil-mist trapping chamber 51, is formedon the right-most region of the separation plate 31. A secondcommunication port 33, which allows the primary oil-mist trappingchamber 51 to communicate with the secondary oil-mist trapping chamber52, is formed on the uppermost region of the separation plate 31. Areturn port 34 is formed at the separation plate 31. The return port 34allows small particle size oil mist (not illustrated) trapped in thesecondary oil-mist trapping chamber 52 to return to the primary oil-misttrapping chamber 51.

As illustrated in FIGS. 2 and 5, the primary oil-mist trapping chamber51 has a bottom surface 51 a. The location of the return port 34 withinthe chamber 51 is located at a higher level than (e.g., verticallyabove) the bottom surface 51 a. Thus, the return port 34 is spacedvertically above and apart from the bottom surface 51 a of the primaryoil-mist trapping chamber 51. The secondary oil-mist trapping chamber 52has a bottom surface 52 a, and the return port 34 is positioned atsubstantially the same level (e.g., same vertical height) as thelowermost portion 52 b of the bottom surface 52 a. Unlike theconventional oil separator, the return port 34 is not located along thebottom surface 51 a of the primary oil-mist trapping chamber 51. Thatis, the return port 34 is located only along the bottom surface 52 a ofthe secondary oil-mist trapping chamber 52. The separation plate 31 hasa wall surface 31 a facing the primary oil-mist trapping chamber 51. Arib 35 is formed near the return port 34 of the wall surface 31 a. Inthis embodiment, the rib 35 has a substantially U-shape such that itprevents the blow-by gas from flowing into the return port 34.

As illustrated in FIG. 2, the upper base 40 is a cover member sized andshaped to cover the separation plate 31 of the middle base 30. Theprimary oil-mist trapping chamber 51 is disposed between the upper base40 and the separation plate 31.

As illustrated in FIG. 2, the lower base 10, the middle base 30, and theupper base 40 are assembled to each other by vibration welding, etc. Theliquid oil trapping chamber 50 and the secondary oil-mist trappingchamber 52 above the liquid oil trapping chamber 50 are positionedbetween the lower base 10 and the middle base 30. The liquid oiltrapping chamber 50 and the secondary oil-mist trapping chamber 52 aredefined by partitions of the lower base 10 and the middle base 30. Theprimary oil-mist trapping chamber 51 is positioned between the middlebase 30 and the upper base 40. The liquid oil trapping chamber 50 is aspace that traps large particle size liquid oil (not illustrated)contained in the blow-by gas.

As illustrated in FIG. 2, the primary oil-mist trapping chamber 51 islocated above the liquid oil trapping chamber 50. The primary oil-misttrapping chamber 51 is hence located downstream of the liquid oiltrapping chamber 50 in a flow passage for the blow-by gas. The primaryoil-mist trapping chamber 51 is a space that traps small particle sizeoil mist contained in the blow-by gas. The secondary oil-mist trappingchamber 52 is located at substantially the same vertical level (e.g.,same vertical height) as the primary oil-mist trapping chamber 51, andit is adjacent to the primary oil-mist trapping chamber 51 in thehorizontal left-to-right direction. The primary oil-mist trappingchamber 51 is separated from the secondary oil-mist trapping chamber 52by the separation plate 31 of the middle base 30. The secondary oil-misttrapping chamber 52 is located downstream of the primary oil-misttrapping chamber 51 in the flow passage of the blow-by gas. Thesecondary oil-mist trapping chamber 52 is a space that traps smallparticle size oil mist contained in the blow-by gas.

The lower base 10, the middle base 30, and the upper base 40 illustratedin FIGS. 1 and 2 are different members made of rigid synthetic resinsuch as polypropylene. The oil separator 1 may be attached in the middleof a flow passage (not illustrated) that connects a crankcase (notillustrated) to an air-intake duct (not illustrated). For example,attaching portions 20 of the lower base 10 and attaching portions 36 ofthe middle base 30 are each attached to a corresponding componentforming the flow passage via a metal collar (not illustrated).

As illustrated in FIGS. 2 and 5, the first flow inlet 11 and the secondflow inlet 12, which are formed in the lower region of the lower base10, each communicate with the flow passage in the crankcase. As aresult, when the blow-by gas flows from the crankcase, it enters throughthe first flow inlet 11 and/or the second flow inlet 12 into the liquidoil trapping chamber 50. The blow-by gas, which thereby flows into theliquid oil trapping chamber 50, then collides with not only interiorwall 10 c of the recess 10 a of the lower base 10, but also collisionwalls 14, 15, 16, 17 and the interior surface of the middle base 30.

As illustrated in FIG. 2, the first collision wall 14 extends upwardfrom an intermediate region of the recess 10 a between the flow inlets11, 12 in the left-to-right direction. The collision wall 14 extendsupward and obliquely above the first flow inlet 11. The second collisionwall 15 extends obliquely below and inward in the horizontal directionfrom a right side of the interior wall 10 c. The third collision wall 16extends inward in the horizontal direction from a left side of theinterior wall 10 c. The third collision wall 16 extends substantiallyparallel to the first collision wall 14, and is positioned above thefirst collision wall 14. The fourth collision wall 17 is located abovethe third collision wall 16, and extends obliquely upward and rightwardfrom an intermediate portion of the collision wall 16. In this manner,the collision wall 17 forms the right portion of a bottom surface of thesecondary oil-mist trapping chamber 52. The collision wall 18 extendscontinuously leftward and upward from the collision wall 17 to form aleft portion of the bottom surface of the secondary oil-mist trappingchamber 52. The collision wall 18 extends obliquely upward and leftwardfrom the collision wall 17 to connect with a left side of the interiorwall 10 a. The sixth collision wall 19 extends downward from an upperwall surface of the interior wall 10 a.

As illustrated in FIG. 2, the large particle size liquid oil containedin the blow-by gas collides with the interior wall 10 c, the collisionwalls 14, 15, 16, 17, and the interior surface of the middle base 30,and thereby adheres to the corresponding surfaces. The large particlesize liquid oil adhered to the interior wall 10 c, collision walls 14,15, 16, 17, and the interior surface of the middle base 30 drops underits own weight (via gravity), and accumulates on the bottom surface 50 aof the liquid oil trapping chamber 50. The accumulated liquid oil thenflows through the flow inlets 11, 12 and is collected. As a result, theliquid oil trapping chamber 50 serves to trap the large particle sizeliquid oil contained in the blow-by gas.

Referring to FIG. 2, the blow-by gas flows from the liquid oil trappingchamber 50, through the first communication port 32, and into theprimary oil-mist trapping chamber 51. The blow-by gas collides with thewall surface 31 a of the separation plate 31 and an interior surface ofthe upper base 40, etc. The small particle size oil mist contained inthe blow-by gas collides with the surfaces and adheres thereto. Thesmall particle size oil mist adhered to the wall surface 31 a, etc.drops due under its own weight (via gravity), and then accumulates onthe bottom surface 51 a of the primary oil-mist trapping chamber 51. Thesmall particle size oil mist subsequently returns to the liquid oiltrapping chamber 50 through the first communication port 32, and then iscollected together with the large particle size liquid oil. Thus, theprimary oil-mist trapping chamber 51 serves to trap the small particlesize oil mist contained in the blow-by gas.

Referring to FIG. 2, the blow-by gas flows from the primary oil-misttrapping chamber 51 through the second communication port 33 into thesecondary oil-mist trapping chamber 52. Here, the blow-by gas collideswith each of the wall surfaces in the secondary oil-mist trappingchamber 52. For example, the blow-by gas collides with the interior wall10 c of the recess 10 a of the lower base 10 within the chamber 52, aswell as each of the collision walls 17, 18, 19, and a back surface 31 bof the separation plate 31, etc. The small particle size oil mistcontained in the blow-by gas collides with the surfaces and adheresthereto. The small particle size oil mist adhered to the surfaces dropsunder its own weight (via gravity), and then accumulates on the bottomsurface 52 a of the secondary oil-mist trapping chamber 52. The smallparticle size oil mist returns to the primary oil-mist trapping chamber51 through the return port 34, and is collected together with the smallparticle size oil mist trapped in the primary oil-mist trapping chamber51. Thus, the secondary oil-mist trapping chamber 52 serves to trap thesmall particle size oil mist contained in the blow-by gas.

As illustrated in FIG. 2, a flow outlet 13 is formed on the upper rightregion of the lower base 10. The flow outlet 13 communicates with thecommunication flow passage of the air-intake duct. Therefore, theblow-by gas flown into the oil separator 1 flows from the secondaryoil-mist trapping chamber 52 through the flow outlet 13 in theair-intake duct. As described above, as blow-by gas flows into the oilseparator 1, large particle size liquid oil and small particle size oilmist contained in the blow-by gas are separated from the blow-by gas anddischarged out of the flow inlets 11, 12. In this way, small particlesize liquid oil and oil mist are prevented from flowing from the flowoutlet 13 of the oil separator 1 into the air-intake duct. As a result,the blow-by gas without the liquid oil and oil mist that were initiallyinput into the separator 1, can be returned as an output from theseparator 1 to the internal combustion engine located downstream of theoil separator 1, to be combusted again in the internal combustionengine.

As described above, the oil separator 1 includes a plurality of oil-misttrapping chambers, for example, a primary oil-mist trapping chamber 51and a secondary oil-mist trapping chamber 52. Therefore, the totallength traversed by the blow-by gas passage within the oil separator 1is relatively long. Such a long length flow passage through the oilseparator offers the potential to enhance the efficiency at which thesmall particle size oil mist contained in the blow-by gas is trapped.

As illustrated in FIG. 2, the return port 34 allows the oil mist trappedin the secondary oil-mist trapping chamber 52 to be returned into theprimary oil-mist trapping chamber 51. The first communication port 32allows the oil mist trapped in the secondary oil-mist trapping chamber52 and the oil mist trapped in the primary oil-mist trapping chamber 51to be returned into the liquid oil trapping chamber 50. The flow inlets11, 12 allow the above-described oil mist and the liquid oil trapped inthe liquid oil trapping chamber 50 to be discharged. In this way, bothoil mist and liquid oil can be collected. Therefore, it is possible tocollect trapped oil mist with the secondary oil-mist trapping chamber 52without providing a dedicated collecting passage, thereby reducing theamount of structural components needed. In addition, the small particlesize oil mist can be efficiently trapped and the size of the oilseparator 1 can be reduced.

As described above, the oil separator 1 includes a separation plate 31,an upstream oil-mist trapping chamber (primary oil-mist trapping chamber51), and a downstream oil-mist trapping chamber (secondary oil-misttrapping chamber 52) as illustrated in FIG. 2. The trapping chambers aredivided by the separation plate 31 and arranged adjacent to each otherin the left-to-right direction. The upstream oil-mist trapping chamber51 fluidly communicates with the flow inlets 11, 12 for blow-by gas viathe liquid oil trapping chamber 50. The downstream oil-mist trappingchamber 52 fluidly communicates with the upstream oil-mist trappingchamber 51, as well as with the flow outlet 13 for blow-by gas. A returnport 34 is formed on the separation plate 31, serving to return the oilmist trapped in the downstream oil-mist trapping chamber 52 to theupstream oil-mist trapping chamber 51. The return port 54 is located ata position vertically above the bottom surface 51 a of the upstreamoil-mist trapping chamber 51 and is positioned at substantially the samevertical height as the lowermost portion of the bottom surface 52 a ofthe downstream oil-mist trapping chamber 52.

The oil contained in blow-by gas is separated from the blow-by gas bythe separator 1, and gathers as droplets in both the upstream oil-misttrapping chamber 51 and the downstream oil-mist trapping chamber 52. Theoil that drops and accumulates in the downstream oil-mist trappingchamber 52 passes through the return port 34 and is allowed to return tothe upstream oil-mist trapping chamber 51. On the other hand, the oilthat drops and accumulates in the upstream oil-mist trapping chamber 51is not allowed to flow through the return port 34 into the downstreamoil-mist trapping chamber 52. Consequently, liquid oil is notaccumulated in the downstream oil-mist trapping chamber 52, and as aresult, the separated liquid oil is prevented from flowing out of thedownstream oil-mist trapping chamber 52 through the flow outlet 13 so asto be discharged outside of the oil separator 1. As a result, the liquidoil can be prevented from flowing to a device(s) such as an internalcombustion engine positioned downstream of the oil separator 1 and frombeing combusted again in the internal combustion engine. In this way,the failure of a device(s) located downstream of the oil separator 1 canbe prevented.

As illustrated in FIG. 2, the separation plate 31 includes the wallsurface 31 a facing opposite to the upstream oil-mist trapping chamber51. The rib 35 is formed in the vicinity of the return port 34 at thewall surface 31 a so that the rib 35 prevents blow-by gas from flowinginto the return port 34. Therefore, blow-by gas is prevented fromflowing from the upstream oil-mist trapping chamber 51 into thedownstream oil-mist trapping chamber 52 through the return port 34.Thus, the blow-by gas tends not to flow through the return port 34 butthrough the communication port 33, which helps to flow the gas from theupstream oil-mist trapping chamber 51 into the downstream oil-misttrapping chamber 52.

As illustrated in FIGS. 2 and 3, the rib 35 has a substantial U-shapedconfiguration. For example, the rib 35 extends circumferentially as anarc around the return port 4. Therefore, the blow-by gas is preventedfrom flowing from the upstream oil-mist trapping chamber 51 through thereturn port 34 into the downstream oil-mist trapping chamber 52.

As illustrated in FIGS. 2 and 3, the rib 35 has a right portion standingupright between the return port 34 and the first communication port 32.Therefore, the right portion of the rib 35 prevents the blow-by gas fromdirectly flowing from the first communication port 32 into the returnport 34. The rib 35 has an upper portion extending from the rightportion along the upper edge of the return port 34 and a lower portionextending from the right portion along the lower edge of the return port34. As a result, the blow-by gas is more reliably prevented from flowingdirectly into the return port 34 from the first communication port 32,and rather flows around the return port 34.

The rib 35 has a substantially U-shape as illustrated in FIG. 2.Alternatively, the rib 35 may have various other shapes such as asubstantially V-shape or a horseshoe shape, to deflect the gas fromflowing into the return port 34. The rib has preferably a shape thatobtains the same effect as that of the substantially U-shaped rib 35.

As described-above, the lower base 10, the middle base 30, and the upperbase 40 are made of resin. Alternatively, the lower base 10, the middlebase 30, and the upper base 40 may be made of separate metal membersthat are integrally connected. Such a metal oil separator generally hasa higher strength and heat resistance as compared to the resin oilseparator 1. As described-above, the lower base 10, the middle base 30,and the upper base 40 are made as separate members. Alternatively, twoor all of these bases may be formed in one member.

As described-above, the oil separator 1 has two oil-mist trappingchambers 51, 52. Alternatively, the oil separator 1 may have more thantwo oil-mist trapping chambers.

The various examples described above in detail with reference to theattached drawings are intended to be representative of the presentdisclosure and are thus non limiting embodiments. The detaileddescription is intended to teach a person of skill in the art to make,use and/or practice various aspects of the present teachings and thusdoes not limit the scope of the disclosure in any manner. Furthermore,each of the additional features and teachings disclosed above may beapplied and/or used separately or with other features and teachings inany combination thereof, to provide improved oil separators, and/ormethods of making and using the same.

What is claimed is:
 1. An oil separator for trapping oil mist containedin blow-by gas, the oil separator comprising: an upstream oil-misttrapping chamber in fluid communication with a flow inlet for blow-bygas; a downstream oil-mist trapping chamber positioned adjacent to theupstream oil-mist trapping chamber and separated from the upstreamoil-mist trapping chamber by a separation plate; a communication port influid communication with the upstream oil-mist trapping chamber and thedownstream oil-mist trapping chamber; a flow outlet configured to allowblow-by gas from the downstream oil-mist trapping chamber to flowoutside of the oil separator; and a return port extending through theseparation plate and configured to allow oil mist trapped in thedownstream oil-mist trapping chamber to return into the upstreamoil-mist trapping chamber; wherein the return port is positioned above abottom surface of the upstream oil-mist trapping chamber and ispositioned at substantially the same height as a lowermost portion of abottom surface of the downstream oil-mist trapping chamber.
 2. The oilseparator of claim 1, wherein the separation plate comprises: a wallsurface facing opposite to the upstream oil-mist trapping chamber; and arib formed on the wall surface proximal the return port, wherein the ribis configured to prevent blow-by gas from flowing from the upstreamoil-mist trapping chamber into the downstream oil-mist trapping chamberthrough the return port.
 3. The oil separator of claim 2, wherein therib has a U-shape configuration and extends along the return port. 4.The oil separator of claim 2, wherein the rib has a U-shapeconfiguration and extends in an arc shape around the return port.
 5. Theoil separator of claim 4, wherein the arc extends more than 180 degreesabout the return port.
 6. An oil separator for trapping oil mistcontained in blow-by gas, the oil separator comprising: a liquid oiltrapping chamber including at least one hole configured to allow liquidoil to exit under the force of gravity; an upstream oil-mist trappingchamber in fluid communication with the liquid oil trapping chamber; adownstream oil-mist trapping chamber positioned adjacent to the upstreamoil-mist trapping chamber and separated from the upstream oil-misttrapping chamber by a separation plate; a communication port configuredto allow the upstream oil-mist trapping chamber to communicate with thedownstream oil-mist trapping chamber; a flow outlet configured to allowblow-by gas from the downstream oil-mist trapping chamber to flowoutside of the oil separator; and a return port formed through theseparation plate and configured to allow oil mist trapped in thedownstream oil-mist trapping chamber to return into the upstreamoil-mist trapping chamber; wherein the return port is positionedvertically above a bottom surface of the upstream oil-mist trappingchamber and is positioned at substantially the same vertical level as alowermost portion of a bottom surface of the downstream oil-misttrapping chamber.
 7. An oil separator for trapping oil mist contained inblow-by gas, the oil separator comprising: a liquid oil trappingchamber; an upstream oil-mist trapping chamber downstream of the liquidoil trapping chamber, wherein the liquid oil trapping chamber is influid communication with a flow inlet for blow-by gas from the upstreamliquid oil trapping chamber; a downstream oil-mist trapping chamberpositioned adjacent to the upstream oil-mist trapping chamber andseparated from the upstream oil-mist trapping chamber by a separationplate; a communication port configured to allow the upstream oil-misttrapping chamber to communicate with the downstream oil-mist trappingchamber; a flow outlet configured to allow blow-by gas from thedownstream oil-mist trapping chamber to flow outside of the oilseparator; and a return port formed through the separation plate suchthat the return port allows oil mist trapped in the downstream oil-misttrapping chamber to return into the upstream oil-mist trapping chamber;wherein the return port is located at a level higher than a bottomsurface of the upstream oil-mist trapping chamber and is positioned atsubstantially the same level as a lowermost portion of a bottom surfaceof the downstream oil-mist trapping chamber.
 8. The oil separator ofclaim 7, wherein the liquid oil trapping chamber includes two holesformed in a bottom portion thereof, wherein the two holes are configuredto allow liquid oil to exit the liquid oil trapping chamber under theforce of gravity.
 9. The oil separator claim 8, wherein the two holesformed in the bottom portion of the liquid oil trapping chamber arelaterally spaced apart.
 10. The oil separator of claim 9, wherein afirst collision wall extends obliquely and upward from proximal a centerof the two holes and forms a barrier for large particle size liquid oilcontained in blow-by gas, wherein the first collision wall is made ofresin material such that the oil adheres thereto.
 11. The oil separatorof claim 7, wherein the separation plate includes a wall surface facingopposite to the upstream oil-mist trapping chamber and a rib formed onthe wall surface proximal the return port such that the rib preventsblow-by gas from flowing from the upstream oil-mist trapping chamberinto the downstream oil-mist trapping chamber through the return port.12. The oil separator of claim 7, wherein the rib has a U-shapeconfiguration and extends about at least a portion of the return port.13. The oil separator of claim 11, wherein the rib has a U-shapeconfiguration and extends circumferentially in an arc shape around thereturn port.
 14. The oil separator of claim 13, wherein the arc extendsangularly more than 180 degrees about the return port.
 15. The oilseparator of claim 11, wherein the rib is formed in a V-shapeconfiguration.
 16. The oil separator of claim 11, wherein the rib isformed in a horseshoe configuration.
 17. The oil separator of claim 7,wherein the liquid oil trapping chamber is positioned adjacent to andimmediately below the downstream oil-mist trapping chamber.
 18. The oilseparator of claim 7, wherein the communication port has a square-shapedvoid configuration.
 19. The oil separator of claim 7, wherein the liquidoil trapping chamber is positioned immediately adjacent to the upstreamoil-mist trapping chamber.
 20. The oil separator of claim 7, wherein thedownstream oil-mist trapping chamber is located laterally adjacent tothe upstream oil mist trapping chamber, and wherein the downstreamoil-mist trapping chamber is located directly above and adjacent to theliquid oil trapping chamber.